The Mercury Four Bolt Carbuertor

The four bolt Holley "teapot" carburetor used on the later Mercury
flatheads confuses many folks. I have even heard these called marine
carburetors. The nice thing about them is they give us a four bolt
intake manifold that will accept some Rochester 2GC carburetors
without an adaptor. Unfortunately, doing this eliminates the vacuum
advance on the stock distributor, just as any carburetor switch does
on a flathead. There were aluminum versions of these manifolds made
in Canada. This photo was provided by one of the regulars at the old
Classicar Flathead Forum.